Artificial disc with post and modular collar

ABSTRACT

An apparatus and method is provided relating to artificial discs. An artificial disc is provided that facilitates simultaneous and independent articulation of flexion/extension, lateral bending, anterior/posterior translation, and axial rotation. The artificial disc provides these four simultaneous and independent articulations by independently addressing each type of articulation in the design of the artificial disc. In one example, an artificial disc is comprised of a bearing disposed between first and second end plates. The bearing is movable relative to each end plate, independent of the other end plate. The end plates are affixed to adjacent vertebrae.

FIELD OF THE INVENTION

This invention relates to the field of surgical implants. In particular,this invention is drawn to artificial discs, artificial discreplacements, and associated methods.

BACKGROUND OF THE INVENTION

The spine can be considered to be a series of joints made up ofvertebrae and discs. Due to trauma, disease, and/or aging, the spine maybe subject to degeneration. This degeneration may destabilize the spineand cause pain and/or nerve damage. Medical procedures are oftenrequired to either ease back pain, repair damage, or to prevent futuredamage.

One procedure that is often used to treat back pain or spinal damage isspinal fusion. Spinal fusion is a surgical technique used to combine twoor more adjacent vertebrae. Supplemental bone tissue is used inconjunction with the patient's natural osteoblastic processes in aspinal fusion procedure. Spinal fusion is used primarily to eliminateback pain caused by the motion of the damaged vertebrae by immobilizingadjacent vertebrae. Conditions for which spinal fusion might be doneinclude degenerative disc disease, treatment of a spinal tumor, avertebral fracture, scoliosis, degeneration of the disc,spondylolisthesis, or any other condition that causes instability of thespine. One problem with a spinal fusion procedure is that, while the twofused vertebrae rarely detach from each other, the fusion procedurecauses additional risk of damage to the adjacent vertebrae. Also, sincethe fused vertebrae can no longer move relative to one another, thespine can no longer provide the motion afforded by a healthy spine.

One alternative to spinal fusion is artificial disc replacement.Artificial disc replacement is a medical procedure in which degeneratedor damaged discs in the spine are replaced with artificial ones. Likewith a spinal fusion, an artificial disc replacement procedure isprimarily used to treat back or neck pain, pain radiating into theextremities, and/or treat a spine damaged from degenerative discdisease. One goal of an artificial disc replacement is to eliminate backpain, while allowing normal spinal motion. One advantage over spinalfusion is that an artificial disc may prevent premature breakdown ofadjacent vertebrae resulting from a spinal fusion procedure. One problemwith artificial disc replacement procedures is that the artificial discdoes not provide the same type of motion that a healthy disc does.Ideally, an artificial disc should allow the vertebral bodies to moverelative to one another in a manner that provides an equivalent motionafforded by a healthy intervertebral disc, in such a way that themovement of the spine approximates the natural movement of a healthyspine. However, typical artificial discs allow some motion, but do notadequately approximate the natural movement of a healthy spine.

There is therefore a need for an artificial disc and related replacementprocedure that adequately treats degenerative disc disease and otherspinal conditions, while also enabling natural spinal articulations.

SUMMARY OF THE INVENTION

A surgical implant configured to be inserted between two vertebrae isprovided including a first member configured to be attachable to a firstvertebrae, the first member having a first concave surface, a secondmember configured to be attachable to a second vertebrae, the secondmember having a second concave surface, a third member disposed betweenthe first and second members, the third member having first and secondconvex surfaces configured to engage the first and second concavesurfaces, respectively, and a protrusion extending from the secondmember at least partially through the third member to restrict themovement of the third member relative to the second member.

One embodiment includes a first member, the first member having a recessformed therein, a second member, the second member having a postextending from the second member, wherein the post extends into therecess of the first member, and a collar disposed between the post andthe recess, wherein the recess and the collar restrict movement of thefirst member relative to the second member.

Another embodiment of the invention provides a method for providing anartificial disc for a spine including providing a first member, forminga recess in the first member, providing a second member, forming a postthat extends from the second member into the recess of the first member,and placing a collar between the post and the recess to restrictmovement of the first member relative to the second member.

Other features and advantages of the present invention will be apparentfrom the accompany drawings and from the detailed description thatfollows below.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and notlimitation in the figures of the accompanying drawings, in which likereferences indicate similar elements and in which:

FIG. 1 is a diagram illustrating the anatomical planes of the body andvarious articulations.

FIG. 2 is a side view showing a portion of a spine with an artificialdisc of the present invention installed between two vertebrae.

FIG. 3 is a side view of the artificial disc of FIG. 2 shown withfasteners in an exploded view.

FIGS. 4 and 5 are exploded isometric views of an artificial disc of thepresent invention.

FIG. 6 is an assembled view of the artificial disc shown in FIGS. 4 and5.

FIG. 7 is an enlarged view of one of the barbed teeth shown in FIG. 6.

FIGS. 8 and 9 are views illustrating exemplary dimensions of theartificial disc 30.

FIG. 10 is and isometric view of the artificial disc, showing in-growthtexture.

FIGS. 11A, 11B, and 11C are isometric diagrams of the artificial disc ofthe present invention, illustrating how the bearing is “nested” betweenthe two end plates.

FIG. 12 is a diagram of the lower end plate and the bearing.

FIGS. 13-16 are sectional diagrams taken along line 13-13 of FIG. 6,with one end plate shown in different positions.

FIGS. 17-19 illustrate an exemplary range of flexion/extensionarticulation of the artificial disc of the present invention.

FIGS. 20-24 are sectional diagrams taken along line 20-20 of FIG. 6,with one end plate shown in different positions.

FIGS. 25-27 are top views of an artificial disc of the presentinvention, illustrating how the artificial disc enables axial rotation.

FIGS. 28-32 are sectional diagrams taken along line 13-13 of FIG. 6 thatillustrate anterior and posterior translation of an artificial disc ofthe present invention.

FIGS. 33-35 are isometric views of an artificial disc of the presentinvention, illustrating three examples of simultaneous and independentdegrees of freedom.

FIG. 36 is an isometric diagram of the end plate and bearing, with thepost and collar shown in dashed lines.

FIG. 37 is an exploded view of an end plate and a collar of the presentinvention.

FIGS. 38 and 39 are sectional diagrams illustrating two examples ofcollars.

FIGS. 40A, 40B, 41A and 41B show additional examples of collars for anartificial disc of the present invention.

FIGS. 42 and 43 are diagrams illustrating an interior collar of thepresent invention.

FIGS. 44-46 are views of an artificial disc of the present inventionwith fixation pegs installed.

FIG. 47 is a sectional view of an artificial disc of the presentinvention, showing details of the peg and locking screw.

FIGS. 48 and 49 are exploded view illustrating how the pegs areinstalled.

FIG. 50 is an isometric view of another example of an artificial disc ofthe present invention

DETAILED DESCRIPTION

The present invention relates to artificial disc replacement and relatedreplacement procedures. The invention introduces the concept of variableconstraint disc replacement, of which there are two components. Thefirst component is immediate fixation (the resistance to displacement ofthe prosthetic endplates in relation to the vertebrae at the time ofinsertion). In one example, this is exemplified in the fixation to theendplates using either barbed teeth alone or with optional peg fixation.While barbed teeth will provide fixation for the majority of motionsegments, use of the peg fixation provides more initial constraint tomotion at the prosthesis-bone interface and thus enhances immediatefixation in the setting where the surgeon is concerned that micromotionmay limit growth of bone in and around the bone-implant interface(osseointegration) and negatively impact long term implant stability(the absence of change of position of the implant on radiographs overtime). Good initial stability at the bone-implant interface has beenrecognized as desireable for the long term success of hip and kneereplacements, and the same concerns exist with any motion preservationdevice. This is particularly true in the spine where neurologic,vascular, and gastrointestinal function can be compromised by migrationof an implant. The ability of a surgeon to compensate for problemsencountered in locally variable anatomy, surgical technique, andpreoperative motion are currently very limited. The design features ofthe present invention address the range of pathology seen in clinicalpractice and avoid catastrophic failure or migration of a particularimplant.

The second component of variable constraint applies to the motion of theprosthesis obtained after implantation at a particular motion segment(segmental motion or articulation). Motion at a particular segment(articulation) varies between levels and varies at the same levelbetween genders, races, age groups, and extent of degeneration(arthritis). Current implants typically take a one motion fits allapproach, which does not reflect the variables mentioned above. In orderto re-create physiologic motion that varies between the particularspinal level and the particular pathology seen at that level, thesurgeon must have options to add or take away constraints to motionintraoperatively. There is a clear precedent in knee arthroplasty wherethe amount of resection of the normal structures in combination with thepre-operative deformity is the major determinant in selecting the amountof constraint required in a prosthetic joint for a particular patient.This concept in joint replacement is sometimes referred to “balance” andreflects a surgeon's attempt to recreate normal range of motionintraoperatively by altering implant components or releasing soft tissuerestraints to motion.

For example, the lumbar segment (articulation) comprised of the disc,ligaments and joints between the fourth and fifth lumbar and also thefourth and fifth cervical vertebrae have been documented to have anincreased propensity for anterior translation with increasingdegeneration. Placement of a disc at these levels that is designed toallow for normal anterior translation that is an average of that seen atmultiple segments may lead, in the long term, to catastrophic failure ofthe implant since the segment tends to have increased motion with ageand degenerative change.

There are reports of this type of failure in some lumbar discreplacements, and an increase in motion above that seen in the normalspine can lead to pain, numbness, and even paralysis. This issue may bemagnified, because in order to insert any prosthetic disc, some of thenormal constraints to motion (the annulus, disc material, posteriorlongitudinal ligament, and uncovertebral ligaments) need to be resectedduring implantation.

Thus, surgeons need to have the ability to tailor constraint to theaccepted definition of normal motion for a particular spinal motionsegment, the amount of normal tissue sacrificed at the time of neuraldecompression or implant insertion, and the pathology visible onpre-operative imaging of the motion segment. The present inventionallows a surgeon to place the implant, take the spine through a normalrange of motion and assess the motion at implant site. Since theinvention is modular, both the height of the inner core and the size andshape of the collar could be changed to decrease or increase motionthrough the replaced disc. Increasing disc height would lead toadditional tension on the soft tissue restraints and limit motion, and alarger collar would restrict translation of the upper prostheticendplate in relation to the lower one. In this manner, a spinal surgeonis enabled to utilize the concept of balanced motion already wellestablished in other joint replacement surgery.

In one example, the invention applies to artificial disc replacementperformed through an anterior approach. Generally, the present inventionprovides an artificial disc configured to attach between two adjacentvertebrae. In one example, the artificial disc is comprised of a firstmember attached is a first vertebrae, a second member attached is asecond adjacent vertebrae, and a third member disposed between the firstand second members (described in detail below). The artificial disc ofthe present invention facilitates simultaneous and independentarticulation of flexion/extension, lateral bending, anterior/posteriortranslation, and axial rotation. An artificial disc of the presentinvention provides these four simultaneous and independent articulationsby independently addressing each type of articulation in the design ofthe artificial disc. In addition, various articulations are constrainedto approximate the natural movement of the spine. Various articulationsare also restricted to prevent damage to the spine, arteries, and nerveswhen excessive stress is applied to the artificial disc.

In order to fully appreciate the following description, it is useful tounderstand various articulations of spinal joints. The articulationswill be described with reference to the anatomical planes of the body.FIG. 1 is a diagram illustrating the three anatomical planes of thebody. The coronal plane 12 (frontal plane) is a vertical plane runningfrom side to side that divides the body, or any of its parts, intoanterior and posterior portions. The sagittal plane 14 (lateral plain)is a vertical plane running from front to back that divides the body, orany of its parts, into right and left sides. When the sagittal plane 14crosses through the midline of the body (as shown in FIG. 1), it dividesthe body or any of its parts into right or left halves, and is known asa median plane. The axial plane 16 (transverse plane) is a horizontalplane that divides the body, or any of its parts, into upper and lowerparts.

FIG. 1 also includes indications various articulations. A first type ofarticulation that is referenced below is flexion-extension.Flexion-extension is a movement from front to back along the sagittalplane 14, such as the movement of nodding your head. Flexion-extensionis illustrated in FIG. 1 by line 20. A second type of articulation thatis referenced below is lateral bending. Lateral bending is a movementfrom side to side (perpendicular to flexion) along the coronal plane 12.Lateral bending is illustrated in FIG. 1 by line 22. A third type ofarticulation that is referenced below is translation. Translation is asliding motion from front to back along the sagittal plane 14 or thetransverse plane 16. This articulation may also be referred to as eitheranterior translation (translation toward the anterior of the body) orposterior translation (translation toward the posterior of the body).Translation is illustrated in FIG. 1 by line 24. A fourth type ofarticulation that is referenced below is axial rotation. Axial rotationis a rotating motion about an axis that is perpendicular to thetransverse plane 16. Axial rotation is illustrated in FIG. 1 by line 26.

FIG. 2 is a side view showing a portion of a spine with an artificialdisc of the present invention installed between two adjacent vertebrae.As shown, an artificial disc 30 is inserted in between a first vertebrae28 and a second vertebrae 29. The artificial disc 30 is comprised offirst and second end plates 36 and 38 and a bearing 40. The first endplate 36 is affixed to the first vertebrae 28. The second end plate 38is affixed to the second vertebrae 29. The end plates 36 and 38 may beattached to the vertebrae in any suitable manner, examples of which aregiven below. The bearing 40 is positioned between the first and secondend plates 36 and 38, and engages each. The bearing 40 is movable invarious ways, relative to the first and second end plates 36 and 38(described in detail below). In addition, the bearing 40 is movablerelative to each end plate, independent of the other end plate. In otherwords, movement of the bearing 40 relative to the first end plate 36 isindependent of movement of the bearing 40 relative to the second endplate 38. These relative and independent movements between the endplates 36 and 38 and the bearing 40 are what allow the artificial disc40 simultaneous and independent articulations of flexion/extension,lateral bending, anterior/posterior translation, and axial rotation.

FIG. 3 is an exploded side view of the spine and artificial disc of FIG.2. In this example, the artificial disc 30 is affixed to the vertebrae28 and 29 using pegs 32 and locking screws 34. The fixation to the boneusing the pegs 32 and locking screws 34 is described in detail below.Generally, after the artificial disc 30 is inserted as shown in FIGS. 2and 3, the surgeon will drill holes through openings formed in theartificial disc 30 and into the vertebrae. Next, the pegs 32 areinserted into the holes. Finally, the locking screws 34 are screwed intothe pegs 32 to lock the pegs 32 in place. Advantages of the pegs overother types of bone fixation include less assembly migration of theimplant, and that the peg is mechanically stronger than a screw of asimilar diameter.

The artificial disc 30 may be made from any suitable material. In oneexample, the first and second end plates are made of a metal such as aCoCr alloy, stainless steel, titanium, etc., or any of these materialscoated with wear resistant material or material treatment, etc. In oneexample, the bearing 40 is made of ultra high molecular weightpolyethylene (UHMWPE), or any other suitable material.

While an artificial disc of the present invention can be configured andimplemented in numerous ways, following are some general guidelineswhich are provided as an example only. For example, the ranges givenbelow are merely examples, as any desired ranges can be implemented.

The bearing of the artificial disc has radii of curvature in both thesagittal and coronal planes. The two curved surfaces, on opposite sidesof the bearing, allow the artificial disc independent and simultaneousflexion/extension and lateral bending. This is described in detailbelow. The curved surfaces, and the inner surfaces of the end platesmaintain a controlled and desired position while allowing motion thatconstrains the device from subluxation.

In this example, flexion/extension articulation in the sagittal plane isunrestricted. At the same time, curved surfaces constrain and preventanterior and posterior subluxation. The configuration of the artificialdisc also allows anterior/posterior translation articulation to beunrestricted over a certain range, and constrained over another range.In one example, anterior/posterior translation is unrestricted withinapproximately +/−0.5 mm and constrained out to approximately +/−1.0 mm.Also in this example, the artificial disc has a nominal 7° anatomicposterior slope with a range of motion of approximately +/−5°.

In this example, lateral bending articulation in the coronal plane isunrestricted. At the same time, curved surfaces constrain and preventmedial lateral subluxation/translation. In one example, the artificialdisc has a lateral bending range of motion of approximately +/−5°.

In this example, axial rotation articulation in the coronal ortransverse planes is restricted and constrained. In one example, theartificial disc has an axial rotation range of motion of approximately+/−5°.

With respect to safety, these exemplary guidelines includeconsiderations relating to sizing, bone fixation, etc. . . . Ideally,the bearing of the artificial disc should be contained safely within theend plates with consideration to failure modes of the device. Withrespect to size and shape of the artificial disc, in one example, theend plates are domed to match anatomic end plate concavity. This convexshape on the end plates will help with the fixation to the vertebrae.Also, the transverse plane footprint of the artificial disc, relative tothe sagittal plane, should be lordosed in the cervical and lumbar spinalregions and kyphosed in the thoracic spinal region to match pureanatomic positioning.

With respect to bone fixation, the first and second end plates mayinclude teeth which are used to resist anterior extrusion. Also, the endplate outer surfaces may include a porous ingrowth interface to help newbone fixation. In one example, peg or screw fixation may be used toresist anterior/posterior or medial/lateral extrusion.

Note that, throughout this description, when terms such as “upper” or“lower” are used, they are relative terms merely used to describe thefigures as oriented in the drawings. For example, if a component isreferred to as an “upper” component, the scope of the invention is notrestricted to that component being used in a literally “upper” position.Likewise, in some potential applications (e.g., a disc replacementprocedure for an animal) where the spine is normally orientedhorizontally, the terms “upper” and “lower” are also relative and do notlimit the scope of the invention.

FIGS. 4 and 5 are exploded isometric views of an artificial disc of thepresent invention. FIG. 4 shows an artificial disc 30, including a firstend plate 36, a second end plate 38, a bearing 40, and a collar 59. FIG.5 shows is the same artificial disc 30, but from another angle, to seethe opposite sides of the end plates 36 and 38 and bearing 40.

The first end plate 36 has a hole 37 formed to facilitate bone fixationusing pegs or screws (described below). The first end plate 36 has aconvex outer surface 42 which, as mentioned above, is configured tomatch the surface of the adjacent vertebrae. The first end plate 36 hasa concave inner surface 44, which, in this example, has a cylindricallycurved shape with closed ends 46. The bearing 40 has a convex uppersurface 48, which has a cylindrically shaped curve. The upper surface 48of the bearing 40 is configured to closely match the inner surface 44 ofthe end plate 36. As is described in detail below, the configuration ofthe interface between the upper surface 48 of the bearing 40 and of theinner surface 44 of the end plate 36 enables the artificial disc 30 tohave flexion/extension articulation.

The second end plate 38 has a hole 39 formed to facilitate bone fixationusing pegs or screws. The second end plate of 38 has a convex outersurface 50 which, like the outer surface 42 of the end plate 36, isconfigured to match the surface of the adjacent vertebrae. The secondend plate 38 also has a concave inner surface 52. However, the concaveinner surface 52 is more complex than the concave inner surface 44 ofthe end plate 36. The inner surface 52 has a middle portion 54 that hasa cylindrically shaped curve, and opposite outer portions 56, which arebowl shaped. Within the inner surface 52, a protrusion or post 58extends upward.

The bearing 40 has a convex lower surface 60. The lower surface 60 ofthe bearing 40 includes a middle portion 62 that has a cylindricallyshaped surface. The middle portion 62 is configured to closely match themiddle portion 54 of the inner surface 52 of the end plate 38 to enableunconstrained lateral bending articulation. However, to facilitateanterior/posterior translation (described in detail below), the width ofthe middle portion 54 of the end plate 38 is greater than the width ofthe middle portion 62 of the bearing 40. This enables unconstrainedtranslation articulation over a range that is approximately equal to thedifference between the width of the middle portions 62 and 52.

A collar 59 is shown between the second end plate 38 and the bearing 40.The collar 59 is configured to fit over the post 58. As described below,different sized and shaped collars may be used to control variousdegrees of change in articulation. Alternately, the post 58 can be sizedas desired, and used without a collar.

The bearing 40 includes a recess 64 formed in the lower surface 60. Therecess 64 is adapted to receive the post 58 and collar 59 when theartificial disc 30 is assembled. In the examples shown in the drawings,the recess 64 does not extend all the way through the bearing 40.However, in other examples, the recess 64 could extend all the waythrough the bearing 40. The recess 64 is larger than the collar 59,which allows the bearing 40 to move over a certain range without thecollar 59 restricting the movement. As described in detail below, thecollar 59, in combination with the recess 64, restricts articulation(lateral bending and anterior/posterior translation) beyond a certainrange. In addition, the collar 59 and recess 64 prevent subluxation ofthe bearing 40.

FIG. 6 is an assembled isometric view of the artificial disc 30 shown inFIGS. 4 and 5 from an anterior direction. As shown, the bearing 40simultaneously engages the end plate 36 and the end plate 38. The outersurfaces 42 and 50 of the end plates 36 and 38 also include a pluralityof barbed teeth 66, configured to prevent anterior expulsion of theartificial disc 30. FIG. 7 is an enlarged view of one of the barbedteeth 66 shown in FIG. 6.

When designing an artificial disc, it is important to consider properfit of the disc, and proper fixation to the bone. If fixation to thevertebrae is not adequate, there is risk of expulsion of the artificialdisc. If the artificial disc does not fit properly (e.g., is too largeor too small), there is also a risk of expulsion, as well as risk ofpain or damage to the spine, arteries, or nerves. Ensuring a proper fitof an artificial disc may require a surgeon to select an artificial dischaving dimensions that most closely fit the patient. In other words, apatient may be fitted with an artificial disc having the dimensionsspecified by the surgeon. Also note that the examples shown in thedrawings illustrate a cervical disc design. Features such as height,width, and footprint would vary, depending on the spinal region orapplication.

FIGS. 8 and 9 are views illustrating exemplary dimensions of theartificial disc 30. FIG. 8 is a side view of the artificial disc 30,with the left edge of the figure being the anterior side of the disc 30.The height of the artificial disc 30 is designated by the letter “H.” Asan example, the height of the artificial disc 30 may fall within therange of 6.5-8.0 mm. FIG. 9 is a bottom view of the artificial disc 30,with the lower edge of the figure being the anterior side. The width andlength of the artificial disc 30 is designated by the letters “W” and“L.” As an example, the length and width of the artificial disc 30 mayfall within the ranges of 17-20 mm and 14-17 mm, respectively. Note thatthese exemplary dimensions are merrily examples, and that the scope ofthe present invention is not limited to these dimensions. As shown, thelength and width of the end plate 38 and 36 control the anatomicfootprint, or parameter profile, of the artificial disc 30. Also notethat the height of the bearing may also vary, as desired.

As mentioned, it is also important that the artificial disc be properlyaffixed to the vertebrae. As mentioned above, the outer surfaces 42 and50 of the end plates 36 and 38, respectively, each have convex domedouter surfaces. These domed surfaces on the end plates match theanatomic end plate concavity of the vertebrae to which they areattached. As mentioned above, the barbed teeth 66 dig into the bone,resisting anterior forces, and provide immediate, mechanicalpost-operative resistance to anterior expulsion. To help the fixation ofthe end plates 36 and 38 to the bones, the outer surfaces 42 and 50 ofthe end plates 36 and 38 can be at least partially coated with porous ingrowth texturing. FIG. 10 is and isometric view of the artificial disc30. The outer surfaces 42 and 50 of the end plates 36 and 38,respectively, has been treated with porous in-growth texturing toprovide longer term bony growth incorporation fixation to the bone. InFIG. 10, the porous in-growth texturing is represented by the shading,and is identified by numeral 68.

Numerous other options are available for supplementing the fixation tothe bone. For example, bone screws or pegs can be used to help securethe end plates to the bone. The example mentioned above of a fixationtechnique using pegs is described in more detail below.

The artificial disc of the present invention includes several safetyfeatures, in addition to those mentioned above. When the artificial discis assembled, the bearing is nested in a pocketed upper and lower endplate. This helps to prevent anterior or posterior expulsion of thebearing and/or the artificial disc. FIGS. 11A, 11B, and 11C are diagramsof the artificial disc 30, illustrating how the bearing 40 is “nested”between the end plates 36 and 38. FIG. 11A shows the end plate 36, withthe upper surface 48 of the bearing 40 nested in the concave innersurface of the end plate 36. FIG. 11B shows the end plate 38, with thelower surface 60 of the bearing 40 nested in the concave inner surfaceof the end plate 38. With respect to the interface between the end plate36 and the bearing 40 (FIG. 11A), the convex surface of the bearing 40fits within the concave surface of the end plate 36. Likewise, withrespect to the interface between the lower end plate 38 and the bearing40 (FIG. 11B), the convex surface of the bearing 40 fits within theconcave surface of the end plate 38. In addition to the bearing beingnested or pocketed between the two end plates, the post 58 of the endplate 38 fits within the recess 64 of the bearing 40. FIG. 11C shows theartificial disc 30 of FIGS. 11A and 11B assembled. FIG. 12 is a diagramof the end plate 38 and the bearing 40. For clarity, the end plate 36 isnot shown, and the post 58, collar 59, and recess 64 are shown in hiddenlines. Since the post 58 and collar 59 are disposed within the recess 64when the artificial disc is assembled, the post 58 and collar 59 willprevent both anterior and posterior expulsion. Also, the collar 59 andrecess 64 restricts movement of the bearing 40 with respect to the endplate 38 (described below).

As mentioned above, flexion/extension articulation in the sagittal planeis unrestricted, while at the same time, curved surfaces of theartificial disc constrain and prevent anterior and posteriorsubluxation. FIGS. 13-16 are sectional diagrams taken along line 13-13of FIG. 6, showing the artificial disc 30, with the end plate 36 shownin different positions. FIGS. 13-14 are sectional diagrams illustratinghow the artificial disc 30 accomplishes flexion/extension articulation.In this example, the interface between the end plate 38 in the bearing40 does not contribute to flexion-extension. As shown, the inner concavesurface 44 of the end plate 36 matches the convex surface 48 of thebearing 40. In the sagittal plane (plane 14 in FIG. 1), the end plate 36is allowed to rotate relative to the bearing 40 to provideflexion/extension articulation (arrow 20 in FIG. 1 and in FIG. 13).FIGS. 13 and 14 show the same artificial disc 30, at different points offlexion/extension. The matching curved surfaces of the end plate 36 andbearing 40 allow unrestricted articulation over the possible range ofmovement.

The configuration of the artificial disc 30 also prevents anterior andposterior subluxation. FIG. 15 is a sectional diagram of the artificialdisc 30 illustrating the position of the end plate 36 in an anteriorsubluxation position. As illustrated, the curves of the end plate 36 andbearing 40 make the subluxation position illustrated in FIG. 15impossible, as is best illustrated by the intersection of the lineswithin the circle 70. Similarly, FIG. 16 is a sectional diagram of theartificial disc 30 illustrating the position of the end plate 36 in aposterior subluxation position. As illustrated, the curves of the endplate 36 and bearing 40 make the subluxation position illustrated inFIG. 16 impossible, as is best illustrated by the intersection of thelines within the circle 72.

The artificial disc 30 facilitates flexion/extension over a range thatis defined by the specific configuration of the artificial disc 30.FIGS. 17-19 illustrate an exemplary range of flexion/extensionarticulation. Of course, the artificial disc 30 can be configured toallow any desired range of motion. FIG. 17 illustrates a neutral ornominal position, which in this example, the end plate 36 is positionedat a 7° angle relative to the end plate 38. FIG. 18 illustrates aforward position, which in this example, the end plate 36 is positionedat a 2° angle relative to the end plate 38. FIG. 19 illustrates abackward position, which in this example, the end plate 36 is positionedat a 12° angle relative to the end plate 38. In this example, theartificial disc 30 has a flexion/extension range of approximately 10°,or 5° each direction from the nominal position.

As mentioned above, lateral bending articulation in the coronal plane isunrestricted, while at the same time, curved surfaces of the artificialdisc constrain and prevent medial lateral subluxation/translation. FIGS.20-22 are sectional diagrams illustrating how the artificial disc 30accomplishes lateral bending articulation. In this example, theinterface between the end plate 36 and the bearing 40 does notcontribute to lateral bending. While the concave inner surface 52 of theend plate 38 does not match the lower surface 60 of the bearing 40, themiddle portion 54 of the concave inner surface 52 and the middle portion62 of the lower surface 60 have the same radius of curvature. In thecoronal plane (plane 12 in FIG. 1), the bearing 40 is allowed to rotaterelative to the end plate 38 to provide lateral bending (arrow 22 inFIG. 1 and in FIG. 20). FIGS. 21 and 22 show the same artificial disc30, at different points of lateral bending.

The curved surfaces making up the middle portions 54 and 62 of the endplate 38 and bearing 40, respectively, allow unrestricted lateralbending articulation over a possible range of movement. Lateral bendingis restricted in the artificial disc 30 by the configuration of thecollar 59 placed over the post 58 of the end plate 38, and the recess 64formed in the bearing 40. The artificial disc 30 is configured to allowunrestricted and unconstrained lateral bending articulation, until awall of the recess 64 engages the collar 59.

The range of lateral bending of the artificial disc 30 is controlled bythe configuration of its components. FIGS. 20-22 illustrate an exemplaryrange of lateral bending articulation. Of course, the artificial disc 30can be configured to allow any desired range of motion. FIG. 20illustrates the artificial disc 30 in a neutral or nominal position.FIG. 21 illustrates lateral bending to one extreme, which in thisexample, is +5° from the position shown in FIG. 20. FIG. 22 illustrateslateral bending to the opposite extreme, which in this example, is −5°from the position shown in FIG. 20. It is evident by looking at FIGS.20-22, at the lateral bending range can be chosen by configuring thespace between the recess 64 and the collar 59. In other words, a largercollar 59, and/or a smaller recess 64, will result in a smaller lateralbending range. Likewise, a smaller collar 59, and/or a larger recess 64will result in a larger lateral bending range.

The configuration of the artificial disc 30 also prevents medial lateralsubluxation. FIGS. 23 and 24 are sectional diagrams of the artificialdisc 30 illustrating the end plate 36 in opposite medial lateralsubluxation positions. As illustrated, the curves of the end plate 38and bearing 40 make the medial lateral subluxation positions, asillustrated in FIGS. 23 and 24, impossible, as is best illustrated bythe intersection of the lines within the circles 74. In addition, thepost 58, and collar 59 also prevent medial lateral subluxation, as isbest illustrated by the intersection of the lines within the circles 74and 76 in FIGS. 23 and 24.

As mentioned above, axial rotation articulation about an axis that isperpendicular to the transverse plane 16 is constrained. FIGS. 25-27 aretop views of an artificial disc 30, illustrating how the artificial disc30 accomplishes axial rotation. In this example, the interface betweenthe end plate 36 and the bearing 40 does not contribute to axialrotation. While the concave inner surface 52 of the end plate 38 doesnot match the lower surface 60 of the bearing 40, the interface betweenthe bearing 40 and end plate 38 allows some degree of rotation. As thebearing 40 rotates relative to the end plate 38, the axial rotation willbe constrained by the curved surfaces of the lower surface 60 of thebearing 40 engaging the curved outer portions 56 of the end plate 38(FIGS. 4 and 5).

The range of axial rotation is controlled by the configuration of thelower surface 60 of the bearing 40 and the concave inner surface 52 ofthe end plate 38. In one example, the allowable axial rotation is +/−5°.FIG. 25 shows the artificial disc 30 in a normal, unrotated position.FIG. 26 shows the artificial disc 30 rotated in one direction by 5°.FIG. 27 shows the artificial disc 30 rotated in the opposite directionby 5°.

FIGS. 28-32 are sectional diagrams taken along line 13-13 of FIG. 6 thatillustrate anterior and posterior translation of an artificial disc ofthe present invention. Referring back to FIGS. 4 and 5, the middleportion 62 of the bearing 40 is narrower than the middle portion 54 ofthe end plate 38. As mentioned above, the middle portions 54 and 62 areeach flat in one direction and share the same curvature radius in theother direction.

FIG. 28 is a sectional diagram of the artificial disc 30 in a neutralposition. As shown, the middle portion 62 of the bearing 40 rests on themiddle portion 54 of the end plate 38. Since the middle portion 62 isnarrower than the middle portion 54, the bearing 40 can slide relativeto the end plate 38, in an anterior and posterior direction. Over arelatively small range, translation articulation is unconstrained.However, the outer portions 56 of the end plate 38 will eventuallyengage the lower surface 60 of the bearing 40 to constrain thetranslation articulation. Furthermore, the post 58 and collar 59restrict anterior and posterior translation when the collar 59 engagesone of the walls of the recess 64. FIG. 29 illustrates anteriortranslation, which is unrestricted up to the point shown in FIG. 29. Asmentioned above, the curvature of the outer portions 56 of the end plate38 will restrict the bearing 40 once the bearing 40 has moved to acertain distance. FIG. 30 illustrates further anterior translation, upto the point where the wall of the recess 64 engages the collar 59.

FIG. 31 illustrates posterior translation, which is also unrestricted upto the point shown in FIG. 31. FIG. 32 illustrates further posteriortranslation, up to the point where the wall of the recess 64 engages thecollar 59. The various dimensions and configurations of the artificialdisc 30 control the range of anterior and posterior translation, and canbe configured to any desired range. In one example, the unrestrictedtranslation range is 0.5 mm in either direction. In this example, theartificial disc 30 is configured such that the collar 59 will engage therecess 64 1 mm in either direction from the neutral position. Of course,various other ranges are also possible.

As described above in shown in figures, an artificial disc of thepresent invention is capable of simultaneous and independentarticulation of flexion/extension, lateral bending, anterior/posteriortranslation, and axial rotation. In addition, various articulations ofthe artificial disc of the present invention are constrained andrestricted, where desired. Each degree of freedom of the artificial discis independently designed to match the needs desired by a user. FIGS.33-35 are isometric views of an artificial disc of the presentinvention, illustrating three examples of simultaneous and independentdegrees of freedom. FIG. 33 shows an example with the flexion/extensionarticulation position at 2° (see FIG. 18), the axial rotation is at +5°(see FIG. 26), the anterior/posterior translation is at +1 mm (see FIG.30), and the lateral bending is at +5° (see FIG. 21). FIG. 34 shows anexample with the flexion/extension articulation position at 7° (see FIG.17), the axial rotation is at 0° (see FIG. 25), the anterior/posteriortranslation is at 0 mm (see FIG. 28), and the lateral bending is at 0°(see FIG. 20). FIG. 35 shows an example with the flexion/extensionarticulation position at 12° (see FIG. 19), the axial rotation is at −5°(see FIG. 27), the anterior/posterior translation is at −1 mm (see FIG.32), and the lateral bending is at −5° (see FIG. 22). It is evident thateach type of articulation can be simultaneously and independentlyachieved with an artificial disc of the present invention.

As described above, the present invention includes the post 58 andcollar 59 extending from the end plate 38 into the recess 64 of thebearing 40 to prevent subluxation of the bearing 40, and to restrict themovement of the bearing 40. Following is a more detailed description ofthe collar 59, including variations of the collar. FIG. 36 is anisometric diagram of an end plate 38 and a bearing 40. For clarity, theopposing end plate 36 is not shown. The post 58 and collar 59 are shownusing hidden lines. The space disposed between the walls of the recess64 and the collar 59 determines the amount of movement the bearing 40can make relative to the end plate 38, before a wall of the recess 64engages the collar 59.

One aspect of the present invention relates to customizing theconfiguration of the artificial disc to suit the needs of a patient.FIG. 37 is an exploded view of the end plate 38 and the collar 59. Asshown, the collar 59 is configured to be placed over the post 58. Inaddition, the collar 59 can interface with the end plate 38 via alocking taper (see FIGS. 38 and 39). Since, in this example, the collar59 is removable, the artificial disc can be used with various types andsizes of collars 59 to achieve the desired amount and type ofarticulation.

In one example, the size (e.g., diameter) of the collar 59 can be variedto achieve a desired result. For example, FIG. 38 is a sectional diagramof an artificial disc 30, similar to the view shown in FIG. 22. FIG. 39is a sectional diagram of the artificial disc 30, with a differentcollar installed. As shown, the collar 80 shown in FIG. 39 is largerthan the collar 59 shown in FIG. 38. As a result, the artificial disc 30shown in FIG. 39 has different articulating characteristics. With alarger collar, such as collar 80, the artificial disc 30 is morerestricted, and will have a shorter articulation range for lateralbending and anterior and posterior translation. Note that theflexion/extension articulation is not affected. A larger collar, such ascollar 80, may be desired for patients who are less stable and who wouldbenefit from a more restrictive disc.

FIGS. 40A and 40B illustrate another collar configuration. FIG. 40A isan isometric diagram showing a collar 82 that has a tapered diameter toprovide various changes in articulations. FIG. 40B is a top view of theartificial disc 30, showing the collar 82, and the recess 64 in dashedlines. FIG. 41A is an isometric diagram showing another collarconfiguration. In this example, the collar 84 is rectangular in shape.The rectangular collar 84 can be configured to either restricttranslation and allow lateral bending, or to allow translation andrestrict lateral bending. FIG. 41B is a top view of the artificial disc30, showing the collar 84, and the recess 64 in dashed lines. As shown,the space between the collar 84 and recess 64 is different on differentsides, since the collar 84 is not symmetrical. In the example shown inFIG. 41B, translation is more restricted than the examples describedabove. If the collar 84 were rotated 90°, lateral bending would be morerestricted. Various other types of collars are also possible for usewith the present invention.

FIG. 42 is a diagram of another type of collar that accomplishes thesame thing as the collars described above. In this example, rather thanproviding a collar that fits around the post 58, an internal collar 86is provided that fits within the walls of the recess 64 of the bearing40. When the bearing 40 moves relative to the end plate 38, the movementwill be restricted once the internal collar 86 comes into contact withthe collar 59. If the collar 59 is not used, then the movement will berestricted once the internal collar 86 comes into contact with the post58. FIG. 43 is a top view of the artificial disc 30, showing theinternal collar 86, collar 59, and post 58 using hidden lines.

As mentioned above while describing FIG. 3, the artificial disc of thepresent invention may be affixed to the vertebrae of the spine usingpegs. After drilling holes into the vertebrae (with the artificial discalready positioned), the pegs 32 are inserted through the openings 37and 39 of the end plates and 36 and 38 and into the holes drilled intothe vertebrae. Once the pegs 32 are in place, locking screws 34 arethreaded into threaded recesses formed in the pegs, to lock the pegs inplace (described in more detail below). One advantage of using the pegs32 rather than typical bone screws, is that bone screws will tend tocause the artificial disc to migrate as the screws are tightened. Byusing pegs 32, this migration is eliminated. The angle of the pegs 32also help to prevent migration, since the pegs are at different anglesfrom one another, and are not parallel to artificial disc.

FIG. 44 is an isometric view of an artificial disc 30, including thepegs 32, and locking screws 34 in an installed position. FIG. 45 is aside view of the artificial disc shown in FIG. 44. FIG. 46 is a frontanterior view of the artificial disc shown in FIG. 44. FIG. 47 is asectional view of the artificial disc shown in FIG. 44, taken alonglines 47-47 of FIG. 46. As shown in FIG. 47, the peg 32 includes annularprotrusions 90 disposed near the end of the peg 32. The hole 39 of theend plate 38 has an annular groove 92 formed in it that is adapted toreceive the annular protrusions 90 of the peg 32. Due to the pluralityof slots 94 formed in the peg 32, the head of the peg is expandable, andthe annular protrusions 90 can snap into the annular groove 92 when thepeg 32 is inserted into the hole 39 of the end plate 38. The lockingscrews 34 are tapered slightly, which causes the peg head to expand whenthe locking screws 34 are screwed into the pegs 32. When the peg headexpands due to the tapered locking screws 34, the annular protrusions 90will be pressed into the annular groove 92, locking the peg 32 in place.The other peg shown in FIG. 47 is installed into the hole 37 of the endplate 36 in the same manner.

FIGS. 48 and 49 are exploded views illustrating the installation of thepegs 32 to the artificial disc 30. FIG. 48 shows a first peg 32 alreadyinstalled into end plate 38. As mentioned above, once the artificialdisc 30 is inserted between two adjacent vertebrae (FIGS. 2 and 3), thesurgeon drills holes into the vertebrae. Next, a peg 32 is inserted intothe hole 37 of the end plate 36, and into the hold drilled in the bone(FIG. 49). Next, a locking screw 34 is screwed into a threaded hole inthe peg 32 (se FIG. 47), locking the peg in place.

As mentioned above, various ways are possible of affixing an artificialdisc of the present invention to the vertebrae. In one example, bonescrews are used in place of pegs. In another example, an artificial discuses bone fixation, and the teeth 66. FIG. 50 is an isometric diagram ofan artificial disc that is similar to the discs described above, butconfigured to use without pegs or bone screws. Also note that the pegand locking screw assembly described above is not limited to artificialdisc. The pegs of the present invention may be used with any desiredtype of surgical implant.

In the preceding detailed description, the invention is described withreference to specific exemplary embodiments thereof. Variousmodifications and changes may be made thereto without departing from thebroader spirit and scope of the invention as set forth in the claims.The specification and drawings are, accordingly, to be regarded in anillustrative rather than a restrictive sense.

1. A surgical implant configured to be inserted between two vertebraecomprising: a first member configured to be attachable to a firstvertebrae, the first member having a first concave surface; a secondmember configured to be attachable to a second vertebrae, the secondmember having a second concave surface; a third member disposed betweenthe first and second members, the third member having first and secondconvex surfaces configured to engage the first and second concavesurfaces, respectively; and a protrusion extending from the secondmember at least partially through the third member to restrict themovement of the third member relative to the second member.
 2. Thesurgical implant of claim 1, wherein the protrusion extends into arecess formed in the third member, and wherein the protrusion and therecess are sized to allow unconstrained lateral bending over a rangebefore being restricted by the protrusion engaging a side wall definedby the recess.
 3. The surgical implant of claim 2, wherein theprotrusion and the recess are sized to allow translation over a rangebefore being restricted by the protrusion engaging a side wall definedby the recess.
 4. The surgical implant of claim 1, wherein the firstconvex surface of the third member and the first concave surface of thefirst member are configured to facilitate flexion/extension of thesurgical implant.
 5. The surgical implant of claim 4, wherein the secondconvex surface of the third member and the second concave surface of thesecond member are configured to facilitate lateral bending, translation,and rotation of the surgical implant.
 6. The surgical implant of claim1, wherein the first and second members are secured to the first andsecond vertebrae by boney adherence to the first and second vertebrae.7. The surgical implant of claim 1, wherein the first and second membersare secured to the first and second vertebrae by a first peg extendingthrough the first member and the first vertebrae and a second pegextending through the second member and the second vertebrae.
 8. Asurgical implant configured to be inserted between two vertebraecomprising: a first member, the first member having a recess formedtherein; a second member, the second member having a post extending fromthe second member, wherein the post extends into the recess of the firstmember; and a collar disposed between the post and the recess, whereinthe recess and the collar restrict movement of the first member relativeto the second member.
 9. The surgical implant of claim 8, wherein thecollar is round.
 10. The surgical implant of claim 8, wherein the collarhas a rectangular shape.
 11. The surgical implant of claim 8, whereinthe collar fits around the protrusion.
 12. The surgical implant of claim8, wherein the size of the collar is configured to restrict articulationof the surgical implant by a desired amount.
 13. The surgical implant ofclaim 8, wherein the collar and the recess are sized to allowunconstrained lateral bending over a range before being restricted bythe collar engaging a side wall defined by the recess.
 14. The surgicalimplant of claim 8, wherein the collar and the recess are sized to allowtranslation over a range before being restricted by the collar engaginga side wall defined by the recess.
 15. A method of providing anartificial disc for a spine comprising: providing a first member;forming a recess in the first member; providing a second member; forminga post that extends from the second member into the recess of the firstmember; and placing a collar between the post and the recess to restrictmovement of the first member relative to the second member.
 16. Themethod of claim 15, further comprising choosing the size of the collarto restrict movement of the first member relative to the second memberby a desired amount.
 17. The method of claim 16, further comprisingselecting a collar from a plurality of different sized collars.
 18. Themethod of claim 15, further comprising choosing the shape of the collarto restrict movement of the first member relative to the second memberin a desired manner.
 19. The method of claim 15, wherein the post,collar, and recess are sized to allow unconstrained lateral bending overa range before being restricted by the configuration of the post,collar, and recess.
 20. The method of claim 15, wherein the post,collar, and recess are sized to allow translation over a range beforebeing restricted by the configuration of the post, collar, and recess.